1. Field of the Invention
The present invention relates to a linear illumination device having a light conducting body and an image reading apparatus using the same.
2. Description of the Related Art
Conventionally, in an illumination device for a facsimile apparatus or an image reading apparatus such as a scanner and a bar code reader, an LED array in which a number of light-emitting devices such as light-emitting diodes are arranged in an array are generally used. (In this application, light-emitting devices such as light-emitting diodes are collectively referred to as LEDs.) In an illumination apparatus with such a structure, a decrease in the number of LEDs to be used in a light source portion causes a decrease and a variation of the illuminance, which makes it difficult to decrease the number of LEDs. Furthermore, since an LED emitting blue light is expensive, it is difficult to reduce fabrication cost.
On the other hand, as a method for decreasing the number of LEDs for the purpose of reducing fabrication cost, a technique of using a light conducting body has been proposed, for example, in Japanese Laid-open Publication No. 8-43633. A structure of an illumination device 100 based on such a conventional technique is shown in FIG. 16.
In an illumination device 100 shown in FIG. 16, one side surface of a bar-shaped light conducting body 101 is provided with a light diffusion portion 102 in parallel with an axis of the light conducting body 101. Illuminants 103 are formed on both ends of the light conducting body 101 so as to be close to light incident surfaces 104a and 104b. Light which is incident upon an inside of the light conducting body 101 from the illuminant 103 travels through the light conducting body 101 in accordance with Snell's law. Light which reaches the light diffusion portion 102 on its way is reflected and diffused by the light diffusion portion 102, and is output from a light-emitting surface 105 opposing the light diffusion portion 102 of the light conducting body 101.
Furthermore, a structure of an image reading apparatus 200 using a conventional illumination device 210 is shown in FIG. 17.
In the illumination device 210 of the image reading apparatus 200 shown in FIG. 17, LEDs 214 are mounted on a printed wiring board 212 as a light source portion, and the LEDs 214 are sealed with a transparent resin 216. The illuminance of the LEDs 214 is determined based on a current flowing therethrough. The level of the current is set by a resistance value of a resistor 218.
Output light 220 from the illumination device 210 passes through a cover glass 222 (which functions as a document table and a cover), is incident upon a surface of an original surface (i.e., a document surface) 224 (subject) to be illuminated, and is reflected from the original surface 224. Reflected light 226 passes through the cover glass 222, and is incident upon a rod lens array 230 fixed by a metal frame 228. An image of the original surface 224 is formed on a photoelectric conversion element 234 mounted on a wiring board 232 by the rod lens array 230.
Furthermore, the printed wiring board 212 on which the LEDs 214 are mounted and the wiring board 232 on which the photoelectric conversion element 234 is mounted are electrically connected to each other via leads 236, for example, with a solder 238.
However, in the above-mentioned conventional illumination device 100 shown in FIG. 16, the illuminants 103 as a light source portion are required to be placed on both ends of the light conducting body 101, which enlarges the size of the device. Therefore, when such an illumination device 100 is used as a contact-type image sensor or the like which is intended to be miniaturized or made compact, inconvenience of enlargement of the entire structure is caused.
Furthermore, the above-mentioned conventional image reading apparatus 200 shown in FIG. 17 uses the leads 236 for electrically connecting the illumination device 210 to the photoelectric conversion element 234. Therefore, particularly in a system in which the three LEDs 214 respectively emitting three colors of light (i.e., red, blue, and green) are used as a light source and a colored original (document) is read by switching between the LEDs, the number of the leads 236 increases, causing inconvenience of complicated wiring. In addition, due to the increase in number of the leads 236, a space for accommodating the wiring therein is required to be enlarged, which hinders miniaturization of an image reading apparatus. Furthermore, when leads with a small diameter are used for the purpose of decreasing an occupied space of the leads 236, it becomes difficult to attach the leads 236 to the wiring boards 212 and 232, and the leads 236 become likely to be cut.